Calculation of air charge amount in internal combustion engine

ABSTRACT

Calculation models ( 22, 24 ) for an in-cylinder air charge amount determine an estimated intake air pressure (Pe) based on an intake air flow rate (Ms), and then determine an air charge amount (Mc) from the estimated intake air pressure (Pe). A correction execution module ( 26 ) corrects, while a vehicle is traveling, the calculation model based on the relationship between the estimated intake air pressure (Pe) and a measured intake air pressure (Ps).

TECHNICAL FIELD

The present invention relates to technology for calculating air chargeamount in an internal combustion engine installed in a vehicle.

BACKGROUND ART

The following two methods are the principal methods used currently todetermine air charge amount in an internal combustion engine. The firstmethod is one that uses intake air flow measured by a flow rate sensor(called an “air flow meter”) disposed on the intake path. The secondmethod is one that uses pressure measured by a pressure sensor disposedon the intake path. A method using a combination of a flow rate sensorand a pressure sensor to calculate air charge amount more accurately hasalso been proposed (JP2001-50090A).

However, measuring instruments such as flow rate sensors and pressuresensors sometimes have appreciably different characteristics amongindividual measuring instruments. Also, accuracy when calculating aircharge amount from measurements taken by a flow rate sensor or apressure sensor is affected by individual differences among constituentelements of internal combustion engines. Also, even in cases where aircharge amount can be calculated correctly at the outset of use of aninternal combustion engine, in some instances accuracy of calculation ofair charge amount may drop due to change over time. Thus, in the past,it was not always possible to calculate accurately the air charge amountin an internal combustion engine.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide technology forcalculating air charge amount of an internal combustion engine withgreater accuracy than the conventional methods.

An aspect of the present invention is a control device for an internalcombustion engine installed in an automobile, wherein the control devicecomprises: a flow rate sensor for measuring fresh air flow in an intakeair passage connected to a combustion chamber of the internal combustionengine; an air charge amount calculation module for calculating aircharge amount to the combustion chamber according to a calculation modelthat includes as parameters measurements by the flow rate sensor andpressure within the intake air passage; a pressure sensor for measuringpressure within the intake air passage; and a correction executionmodule for correcting the calculation model based on measurement by theflow rate sensor and measurement by the pressure sensor.

With this device, since the calculation model is corrected on the basisof measurements by a flow rate sensor and a pressure sensor, error dueto individual differences among constituent elements of internalcombustion engine or to change over time can be compensated for. As aresult, it is possible to calculate air charge amount with greateraccuracy than the conventional device.

The present invention can be embodied in various forms, for example, aninternal combustion engine control device or method; an air chargeamount calculation device or method; a engine or vehicle equipped withsuch a device; a computer program for realizing the functions of such adevice or method; a recording medium having such a computer programrecorded thereon; or various other forms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram depicting the arrangement of a controldevice as an embodiment of the present invention.

FIG. 2 is a diagram depicting adjustment of opening/closing timing ofthe intake valve 112 by the variable valve mechanism 114.

FIG. 3 is a block diagram depicting the arrangement of the in-cylinderintake air amount calculation module 18.

FIGS. 4(A) and 4(B) illustrate an example of the intake piping model andthe intake valve model 24.

FIG. 5 is a flowchart illustrating the model correction procedure inEmbodiment 1.

FIG. 6 is a diagram depicting an example of the correction processes inSteps S4 and S5.

FIG. 7 is a flowchart illustrating the model correction procedure inEmbodiment 2.

FIG. 8 is a diagram depicting calculation error in estimated intake airpressure Pe caused by error in intake air flow rate Ms measured by theair flow meter 130.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the invention are described hereinbelow on the basisof embodiments, in the indicated order.

-   A. Device Arrangement-   B. Embodiment 1 of Calculation Model Correction-   C. Embodiment 2 of Calculation Model Correction-   D: Variant Examples:    A. Device Arrangement

FIG. 1 is a conceptual diagram depicting the arrangement of a controldevice as an embodiment of the present invention. This control device isconfigured as a device for controlling a gasoline engine 100 installedin a vehicle. The engine 100 comprises an intake air line 110 forsupplying air (fresh air) to the combustion chamber, and an exhaust line120 for expelling exhaust to the outside from the combustion chamber.Within the combustion chamber are disposed a fuel injection valve 101for injecting fuel into the combustion chamber, a spark plug 102 forigniting the mixture in the combustion chamber, an intake valve 122, andan exhaust valve 122.

On the intake air line 110 are disposed, in order from the upstream end,an air flow meter 130 (flow rate sensor) for measuring intake air flowrate; a throttle valve for adjusting intake air flow rate; and a surgetank 134. In the surge tank 134 are disposed a temperature sensor 136(intake air temperature sensor) and a pressure sensor 138 (intake airpressure sensor). Downstream from the surge tank 134, the intake airpassage splits into a plurality of branch lines connected to theplurality of combustion chambers; in FIG. 1 however, for the sake ofsimplicity only one branch line is shown. On the exhaust line 120 aredisposed an air-fuel ratio sensor 126 and a catalyst 128 for eliminatingharmful components in exhaust gases. It is possible for the air flowmeter 130 and the pressure sensor 138 to be situated at other locations.In this embodiment, fuel is injected directly into the combustionchamber, but it would be acceptable as well to inject the fuel into theintake air line 110.

The engine 100 is switched between intake operation and exhaustoperation by means of opening and closing of the intake valve 112 andthe exhaust valve 122. The intake valve 112 and the exhaust valve 122are each provided with a variable valve mechanism 114, 124 for adjustingopening/closing timing. These variable valve mechanisms 114, 124 featurevariable length of the open valve time period (so-called working angle)and position of the open valve time period (termed the “phase of theopen valve time period” or the “VVT (Variable Valve Timing) position”).As variable valve mechanisms it would be possible to employ, forexample, that disclosed in JP2001-263015A filed by the Applicant.Alternatively, it would be possible to use a variable valve mechanismthat uses an electromagnetic valve to vary the working angle and phase.

Operation of the engine 100 is controlled by the control unit 10. Thecontrol unit 10 is constituted as a microcomputer comprising an internalCPU, RAM, and ROM. Signals from various sensors are presented to thecontrol unit 10. In addition to the aforementioned sensors 136, 138, and126, these sensors include a knock sensor 104, a water temperaturesensor 106 for sensing engine water temperature, a revolution sensor 108for sensing engine revolution, and an accelerator sensor 109.

In memory (not shown) in the control unit 10 are stored a VVT map 12 forestablishing the phase of the open valve time period (i.e. the VVTposition) of the intake valve 12, and an working angle map 14 forestablishing the working angle of the intake valve 112. These maps areused for setting operating status of the variable valve mechanisms 114,124 and the spark plug 102 with reference to engine revolution, load,engine water temperature and so on. Also stored in memory in the controlunit 10 are programs for executing the functions of a fuel feed controlmodule 16 that controls the fuel feed rate to the combustion chamber bythe fuel injection valve 101, and of an in-cylinder intake air amountcalculation module 18.

FIG. 2 is a diagram depicting adjustment of opening/closing timing ofthe intake valve 112 by the variable valve mechanism 114. With thevariable valve mechanism 114 of this embodiment, the length of the openvalve time period (working angle) θ is adjusted by means of changing thelift level of the valve shaft. The phase of the open valve time period(center of the open valve time period) φ is adjusted using the VVTmechanism (variable valve timing mechanism) belonging to the variablevalve mechanism 114. This variable valve mechanism 114 enables intakevalve 112 working angle and open valve time period phase to be modifiedindependently. Accordingly, intake valve 112 working angle and openvalve time period phase can each be set to respectively favorableconditions, with reference to engine 100 operating conditions. Thevariable valve mechanism 124 of the exhaust valve 122 has the samefeatures.

B. Embodiment 1 of Calculation Model Correction

FIG. 3 is a block diagram depicting the arrangement of the in-cylinderintake air amount calculation module 18. The in-cylinder intake airamount calculation module 18 includes an intake piping model 22, anintake valve model 24, and a correction execution module 26. The intakepiping model 22 is a model for calculating an estimated value Pe forintake air pressure (hereinafter termed “estimated intake air pressure”)in the surge tank 134 on the basis of the output signal Ms of the airflow meter 130. The intake valve model 24 is a model for calculatingin-cylinder air charge amount Mc on the basis of this estimated intakeair pressure Pe. Here, “in-cylinder air charge amount Mc” refers to theamount of air introduced into the combustion chamber during a singlecombustion cycle of the combustion chamber. The correction executionmodule 26 executes correction of the intake valve model 24 on the basisof intake air pressure Ps measured by the pressure sensor 138 (termed“measured intake air pressure”) and estimated intake air pressurederived with the intake piping model 22.

FIGS. 4(A) and 4(B) illustrate an example of the intake piping model andthe intake valve model 24. This intake piping model 22 calculatesestimated intake air pressure Pe using as inputs, in addition to theintake air flow rate Ms, the in-cylinder air charge amount Mc# at thetime of the previous calculation (described later) and the intake airtemperature Ts. The intake piping model can be represented by thefollowing Eq. (1), for example.

$\begin{matrix}{\frac{\mathbb{d}P_{e}}{\mathbb{d}t} = {\frac{{RT}_{s}}{V}\left( {M_{s} - M_{c}} \right)}} & (1)\end{matrix}$

Here, Pe denotes estimated intake air pressure, t denotes time, Rdenotes the gas constant, Ts denotes intake air temperature, V denotestotal volume of the intake air line downstream from the air flow meter130, Ms denotes intake air flow rate (mol/sec) measured by the air flowmeter 130, and Mc is a value derived by converting in-cylinder aircharge amount to flow rate (mol/sec) per unit of time. When Eq. (1) isintegrated, estimated intake air pressure Pe is given by Eq. (2).

$\begin{matrix}\begin{matrix}{P_{e} = {\int\ {\mathbb{d}P_{e}}}} \\{= {\int{\frac{{RT}_{s}}{V}\left( {M_{s} - M_{c}} \right)\ {\mathbb{d}t}}}} \\{= {{k\frac{{RT}_{s}}{V}\left( {M_{s} - M_{c}^{\#}} \right)\Delta\; t} + P_{c}^{\#}}}\end{matrix} & (2)\end{matrix}$

Here, k is a constant, Δt denotes the period for performing calculationwith Eq. (2), Mc# denotes in-cylinder air charge amount at the time ofthe previous calculation, and Pe# denotes estimated intake air pressureat the time of the previous calculation. Since the values on the rightside of Eq. (2) are known, according to Eq. (2) estimated intake airpressure Pe can be calculated for a given time interval Δt.

In preferred practice the intake air temperature Ts may be measured bythe temperature sensor 136 (FIG. 1) disposed in the intake air line 110;however, measurement by another temperature sensor that measures outsideair temperature may be used as the intake air temperature Ts instead.

The intake valve model 24 has a map indicating the relationship betweenestimated intake air pressure Pe and charge efficiency ηc. That is,charge efficiency ηc can be derived when estimated intake air pressurePe given by the intake piping model 22 is input into the intake valvemodel 24. As is well known, charge efficiency ηc is proportional to thein-cylinder air charge amount Mc in accordance with Eq. (3)M _(c) =k _(c) ·η _(c)  (3)

Here, kc is a constant. Plural maps of the relationship betweenestimated intake air pressure Pe and charge efficiency ηc are preparedwith reference to operating conditions (Nen, θ, φ), with the appropriatemap being selected depending on operating conditions. In thisembodiment, the operating conditions used in the intake valve model 24are defined by three operating parameters, namely, engine revolutionNen, and the working angle θ and phase φ (FIG. 2) of intake valve 112.

FIG. 4(B) shows an example of a map of the intake valve model 24 havingworking angle θ as a parameter. Here, a relationship between estimatedintake air pressure Pe and charge efficiency ηc is established for eachworking angle θ. By using such a map, charge efficiency ηc can bederived from estimated intake air pressure Pe.

In the intake valve model 24, since charge efficiency ηc is dependent onthe parameters Pe, Nen, θ, and φ, charge efficiency ηc is a function ofthese parameters, as indicated by Eq. (4) following.η_(c)=η_(c)(P _(e) , N _(en), θ, φ)  (4)

In-cylinder air charge amount Mc can be written as Eq. (5) below, forexample.

$\begin{matrix}{M_{c} = {{k_{c} \cdot \eta_{c}} = {\frac{T_{s}}{T_{c}}\left( {{k_{a} \cdot P_{e}} - k_{b}} \right)}}} & (5)\end{matrix}$

Here, Ts denotes intake air temperature, Tc denotes in-cylinder gastemperature, and ka and kb are coefficients. These coefficients ka, kbare values established with reference to operating conditions (Nen, θ,φ). Where Eq. (5) is used, it is possible to derive charge efficiency ηcfrom estimated intake air pressure Pe, using measured or estimatedvalues for intake air temperature Ts and in-cylinder gas temperature Tc,and parameters ka, kb determined with reference to operating conditions.

It is possible to calculate in-cylinder air charge amount Mc using Eq.(2) and Eq. (5) given previously. In this case, estimated intake airpressure Pe is first calculated in accordance with the intake pipingmodel 22 of Eq. (2). At this time, the value of in-cylinder air chargeamount Mc# derived in accordance with the intake valve model 24 of Eq.(5) at the time of the previous calculation is used. Then, using thisestimated intake air pressure Pe, current in-cylinder air charge amountMc (or charge efficiency ηc) is calculated in accordance with the intakevalve model 24 of Eq. (5).

From the preceding description it will be understood that with thecalculation models of the embodiment, calculation of estimated intakeair pressure Pe by means of the intake piping model 22 utilizes thecalculation result Mc# of the intake valve model 24. Accordingly, whenan error occurs in the intake valve model 24, an error will be producedin the estimated intake air pressure Pe as well.

Where an intake valve having a variable valve mechanism is employed,there is a high likelihood that the intake valve model 24 will changeover time. One reason for this is that deposits form in the gap betweenthe valve body of the intake valve and the intake port of the combustionchamber, as a result of which the relationship of valve opening and flowpassage resistance changes. Such change over time in flow passageresistance at the valve location has a particularly appreciable effectunder operating conditions in which the working angle φ (FIG. 2) issmall. On the other hand, with an ordinary valve not equipped with avariable valve mechanism (i.e. a valve performing on/off operationonly), since the working angle φ does not change, such problems areinfrequent. Accordingly, change over time in flow passage resistance atthe valve location represents a greater problem in variable valvemechanisms.

Among variable valve mechanisms with variable working angle φ, there area first type wherein the working angle φ changes depending on change inlift as depicted in exemplary fashion in FIG. 2; and a second typewherein only the working angle φ changes, with lift held constant at itsmaximum value. Change over time in flow passage resistance at the valvelocation is particularly notable in variable valve mechanisms of thefirst type.

In this way, there occur instances in which error is produced in theintake piping model 22 and the intake valve model 24, due to change overtime in the intake system of the engine. In some instances error may beproduced in the intake piping model 22 and the intake valve model 24 dueto individual differences in engines or individual differences amongsensors 130, 138 as well. Accordingly, in the embodiment, such errorsare compensated for by correcting the models 22, 24, during operation ofthe vehicle.

FIG. 5 is a flowchart illustrating the routine for executing correctionof the calculation model for in-cylinder air charge amount Mc inEmbodiment 1. This routine is repeated at predetermined time intervals.

In Step S1, the correction execution module 26 determines whetheroperation of the engine 100 is in a steady state. Here, “steady state”refers to substantially constant revolution and load (torque) of theengine 100. Specifically, the engine may be determined to be in a“steady state” when engine revolution and load remain within a range of±5% of their respective average values during a predetermined timeinterval (of 3 seconds, for example).

When the engine is determined not to be in a steady state, the routineof FIG. 5 is terminated, whereas if determined to be in a steady state,the correction process beginning with Step S2 is executed. In Step S2,estimated intake air pressure Pe is derived in accordance with theintake piping model 22 on the basis of intake air flow rate Ms (FIG. 3)measured by the air flow meter 130, and this is compared with measuredintake air pressure Ps measured by the pressure sensor 138. In the eventthat the estimated intake air pressure Pe is less than the measuredintake air pressure Ps, the correction process of Step S4 is executed,and in the event that the estimated intake air pressure Pe is greaterthan the measured intake air pressure Ps, the correction process of StepS5 is executed.

FIG. 6 is a diagram depicting an example of the correction processes inSteps S4 and S5. The drawing depicts the characteristics of the intakevalve model 24, with the horizontal axis denoting intake air pressure Peand the vertical axis denoting charge efficiency ηc. In the event that acorrection process is carried out, since the engine 100 is in a steadystate, the intake air flow rate Ms measured by the air flow meter 130will be proportional to the in-cylinder air charge amount Mc.Accordingly, the value of charge efficiency ηc can be derived bydividing the intake air flow rate Ms measured by the air flow meter 130,by a predetermined constant. Since this charge efficiency ηc (=Mc/kc) isused when deriving estimated intake air pressure Pe by theaforementioned Eq. (2), the relationship between charge efficiency ηcand estimated intake air pressure Pe in the intake valve model 24 lieson the initial characteristic curve prior to correction (shown by thesolid line). In some instances, however, measured intake air pressure Psmay not coincide with this estimated intake air pressure Pe. In suchinstances, in Step S4 or S5, the characteristics of the intake valvemodel 24 are corrected so that estimated intake air pressure Pe nowcoincides with measured intake air pressure Ps. Specifically, as shownby way of example in FIG. 6, where estimated intake air pressure Pe isless than measured intake air pressure Ps, in Step S4 the intake valvemodel 24 is adjusted so as to increase estimated intake air pressure Pe.Where estimated intake air pressure Pe is greater than measured intakeair pressure Ps, on the other hand, in Step S5 the intake valve model 24is adjusted so as to decrease estimated intake air pressure Pe. In theembodiment, since the intake valve model 24 is represented by Eq. (5),correction of the intake valve model 24 means adjusting the coefficientska, kb.

In Step S6, the intake valve model 24 corrected in this manner is storedon a per-operating condition basis. Specifically, coefficients ka, kb ofEq. (5) are associated with the operating conditions at the time thatthe routine of FIG. 5 is executed, and stored in nonvolatile memory (notshown) in the control unit 10. Subsequently, since the corrected modelis used, in-cylinder air charge amount Mc can be calculated with greateraccuracy. During vehicle operation it is common for engine revolutionand load to vary gradually. In such instances as well, by utilizing thecorrected models 22, 24, it is possible to correctly calculatein-cylinder air charge amount Mc on the basis of measured intake airflow rate Ms measured by the air flow meter 130.

Corrections made to an in-cylinder intake air amount calculation modelunder given operating conditions may be applied to the coefficients ka,kb for other similar operating conditions. For example, when thecharacteristics of in-cylinder intake air amount calculation models 22,24 are associated with operating conditions specified in terms of threeoperating parameters (engine revolution Nen, intake valve working angleθ, and phase φ of the open valve time period of the intake valve), thecharacteristics of the in-cylinder intake air amount calculation modelsat other operating conditions wherein the operating parameters arewithin a range of ±10% may be subjected to correction at the same orsubstantially the same correction level. By so doing, it is possible tocorrect appropriately in-cylinder intake air amount calculation modelsat other similar conditions.

In the above manner, according to Embodiment 1, when the engine is in asubstantially steady state during vehicle operation, the in-cylinderintake air amount calculation model is corrected on the basis ofcomparison of estimated intake air pressure Pe with measured intake airpressure Ps, whereby it is possible to compensate for error caused byindividual differences among engines or sensors and other components, orby change over time in flow passage resistance at the valve location. Asa result, accuracy of measurement of in-cylinder intake air amount canbe improved on an individual vehicle basis.

C. Embodiment 2 of Calculation Model Correction

FIG. 7 is a flowchart illustrating the in-cylinder air charge amount Mccalculation model correction procedure in Embodiment 2. This routine hasan additional Step S10 coming between Step S1 and Step S2 in the routineof Embodiment 1 depicted in FIG. 5.

In Step S10, intake air flow rate Ms-measured by the air flow meter 130is compensated. Specifically, the air flow meter 130 is corrected sothat, under steady state operating conditions, the air-fuel ratiomeasured by the air-fuel ratio sensor 126 (FIG. 1), the fuel injectionamount by the fuel injection valve 101, and the intake air flow rate Ms(=Mc) measured by the air flow meter 130 are matched. In the processbeginning with Step S2, correction of the in-cylinder intake air amountcalculation models is executed in the same manner as in Embodiment 1,using the measured intake air flow rate Ms measured by the air flowmeter 130.

FIG. 8 depicts calculation error in estimated intake air pressure Pecaused by error in intake air flow rate Ms measured by the air flowmeter 130. Here, since it is assumed that the engine is in a steadystate operating condition, the measured intake air flow rate Ms measuredby the air flow meter 130 is proportional to the in-cylinder air chargeamount Mc (i.e. charge efficiency ηc). As described in FIGS. 3, 4(A) and4(B), the estimated intake air pressure Pe derived with the intakepiping model 22 is determined on the basis of this measured intake airflow rate Ms. Accordingly, if measured intake air flow rate Ms deviatesfrom the true value, error (deviation) will be produced in estimatedintake air pressure Pe. Such deviation in estimated intake air pressurePe produces calculation error of in-cylinder air charge amount Mc duringnormal operation. Accordingly, in Embodiment 2, prior to correcting thein-cylinder air charge amount Mc calculation model, the air flow meter130 is corrected so as to obtain the correct intake air flow rate Ms. Asa result, the in-cylinder air charge amount Mc can be calculated withgreater accuracy.

Correction of the air flow meter 130 (typically an intake air flow ratesensor) may be carried out on the basis of output of some other sensorbesides the air-fuel ratio sensor. For example, correction of the intakeair flow rate sensor could be carried out on the basis of torquemeasured by a torque sensor (not shown).

D: VARIANT EXAMPLES

The invention is not limited to the embodiments and embodimentsdescribed hereinabove, and may be reduced to practice in various otherforms without departing from the spirit thereof, such as the variantexamples described below, for example.

D1: Variant Example 1

Equations (1)–(5) of the in-cylinder air charge amount model used in theembodiments are merely exemplary, it being possible to use various othermodels instead. Also, it is possible to use parameters other than thethree parameters mentioned hereinabove (engine revolution Nen, intakevalve working angle θ, and phase φ of the open valve time period of theintake valve), as operating parameters for specifying operatingconditions associated with the in-cylinder air charge amount model. Forexample, the working angle of the exhaust valve or the phase of the openvalve time period thereof may be used as operating parameters forspecifying operating conditions.

D2: Variant Example 2

Whereas in the embodiments hereinabove there is employed a model thatderives an estimated value Pe of intake air pressure Ps measured by thepressure sensor 138 from measured intake air flow rate Ms measured bythe air flow meter 130, and calculate in-cylinder air charge amount Mcfrom this estimated value Pe, it would be possible to use some othercalculation model instead. Specifically, it would be possible to employ,as the calculation model for in-cylinder air charge amount, a model thatestimates pressure within the intake air passage from some parameterother than flow rate measured by a flow rate sensor, and that calculatesin-cylinder air charge amount using the estimated pressure and flow ratesensor measurements as parameters.

Additionally, whereas in the preceding embodiments correction ofcalculation models involved deriving an estimated value Pe for intakeair pressure Ps measured by the pressure sensor 138, correction ofcalculation models on the basis of pressure Ps, Pe may be carried out bysome other method instead. More generally, correction of calculationmodels can be executed on the basis of the output signal of a flow ratesensor for measuring intake air flow rate, and the output signal of apressure sensor for measuring pressure on the intake piping. Correctionof calculation models in this way will preferably be carried out withthe engine in a substantially steady state operating condition, buttypically can also be carried out during vehicle operation.

D3: Variant Example 3

The present invention is not limited to internal combustion enginesequipped with a variable valve mechanism, but is applicable also tointernal combustion engines whose valve opening characteristics cannotbe modified. However, as illustrated in Embodiment 1, the advantages ofthe invention are particularly notable in internal combustion enginesequipped with a variable valve mechanism.

INDUSTRIAL APPLICABILITY

The invention is applicable to a control device for internal combustionengines of various kinds, such as gasoline engines or diesel engines.

1. A control device for an internal combustion engine installed in avehicle, comprising: a flow rate sensor for measuring fresh air flowrate in an intake air passage connected to a combustion chamber of theinternal combustion engine; a pressure sensor for measuring pressurewithin the intake air passage; an air charge amount calculation module,comprised of an intake piping model, an intake valve model and acorrection execution module for calculating air charge amount to thecombustion chamber according to a calculation model that includes asparameters measurement by the flow rate sensor and pressure within theintake air passage; and the correction execution module for correctingthe calculation model based on measurement by the flow rate sensor andmeasurement by the pressure sensor, wherein the calculation model is amodel wherein the intake piping model estimates pressure within theintake air passage based on an output signal of the flow rate sensor,and the intake valve model utilizes the estimated pressure to calculateair charge amount to the combustion chamber, and the correctionexecution module executes correction of the intake valve model by adifference between the estimated pressure and pressure measured by thepressure sensor.
 2. A control device according to claim 1, wherein theinternal combustion engine comprises a variable valve mechanism enablingmodification of flow passage resistance at a location of an intake valveby means of changing a working angle of the intake valve, andrelationships of pressure within the intake air passage to the aircharge amount in the computation model are established with reference tooperating conditions specified in terms of a plurality of operatingparameters that include the working angle of the intake valve.
 3. Acontrol device according to claim 2, wherein the correction executionmodule, by means of executing correction of the calculation model,compensates for error concerning relationship between size of theworking angle of the intake valve and flow passage resistance at theintake valve location.
 4. A control device according to claim 1, furthercomprising: a fuel feed controller for controlling a feed amount of fuelflowing into the combustion chamber; and an air-fuel ratio sensordisposed on an exhaust passage connected to the combustion chamber,wherein the correction execution module is able to correct the flow ratesensor according to a measured air-fuel ratio so that the measuredair-fuel ratio measured by the air-fuel ratio sensor, the fuel feedamount established by the fuel feed controller, and the air chargeamount determined based on the output signal of the flow rate sensor areconsistent with one another, and correction of the calculation model isexecuted after correction of the flow rate sensor.
 5. A control deviceaccording to claim 1, wherein the correction execution module executesthe correction during a period in which revolution and load of theinternal combustion engine are substantially constant.
 6. A method forcalculating air charge amount in an internal combustion engine installedin a vehicle, comprising: (a) providing a flow rate sensor for measuringfresh air flow rate in an intake air passage connected to a combustionchamber of the internal combustion engine, and a pressure sensor formeasuring pressure within the intake air passage; (b) calculating aircharge amount to the combustion chamber according to a calculation modelthat includes as parameters measurement by the flow rate sensor andpressure within the intake air passage; and (c) correcting thecalculation model based on measurement by the flow rate sensor andmeasurement by the pressure sensor, wherein the calculation model is amodel that estimates pressure within the intake air passage based on anoutput signal of the flow rate sensor as input into an intake pipingmodel, and utilizes the estimated pressure as input into an intake valvemodel to calculate air charge amount to the combustion chamber, and thestep (c) includes a step of executing correction of the intake valvemodel by a difference between the estimated pressure and pressuremeasured by the pressure sensor coincide.
 7. A method according to claim6 wherein the internal combustion engine comprises a variable valvemechanism enabling modification of flow passage resistance at a locationof an intake valve by means of changing a working angle of the intakevalve, and relationships of pressure within the intake air passage tothe air charge amount in the computation model are established withreference to operating conditions specified in terms of a plurality ofoperating parameters that include the working angle of the intake valve.8. A method according to claim 7 wherein the step (c) includescompensating for error concerning relationship between size of theworking angle of the intake valve and flow passage resistance at theintake valve location, by means of executing correction of thecalculation model.
 9. A method according to claim 6 wherein the internalcombustion engine further comprises: a fuel feed controller forcontrolling a feed amount of fuel flowing into the combustion chamber;and an air-fuel ratio sensor disposed on an exhaust passage connected tothe combustion chamber, wherein the step (c) includes the steps of:correcting the flow rate sensor according to a measured air-fuel ratioso that the measured air-fuel ratio measured by the air-fuel ratiosensor, the fuel feed amount established by the fuel feed controller,and the air charge amount determined based on the output signal of theflow rate sensor are consistent with one another; and executingcorrection of the calculation model after correction of the flow ratesensor.
 10. A method according to claim 6 wherein the correction in thestep (c) is executed during a period in which revolution and load of theinternal combustion engine are substantially constant.
 11. A controldevice for an internal combustion engine installed in a vehicle,comprising: a first sensor for measuring a parameter which is usable toestimate pressure within an intake air passage; a second sensor formeasuring pressure within the intake air passage; and a correctionexecution module for correcting air charge amount to the combustionchamber, calculated by an intake valve model, based on pressureestimated by an intake piping model from the parameter measured by thefirst sensor and pressure measured by the second sensor.
 12. A controldevice for an internal combustion engine installed in a vehicle,comprising: a first sensor for measuring a parameter which is usable toestimate pressure within an intake air passage; a second sensor formeasuring pressure within the intake air passage; and a correctionexecution module for correcting air charge amount to the combustionchamber, calculated by an intake valve model, based on the parametermeasured by the first sensor and pressure measured by the second sensor,wherein the correction execution module executes the correction of theair charge amount to the combustion chamber after executing correctionof the first sensor.